Some designs of mobile communication devices—such as smart phones, tablet computers, and laptop computers—contain one or more Subscriber Identity Module (SIM) cards that provide users with access to multiple separate mobile telephony networks. Examples of mobile telephony networks include Third Generation (3G), Fourth Generation (4G), Long Term Evolution (LTE), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Wideband CDMA (WCDMA), Global System for Mobile Communications (GSM), and Universal Mobile Telecommunications Systems (UMTS). A public land mobile network (PLMN) is a mobile telephony network controlled by a specific network operator. A PLMN may be defined by a unique combination of a mobile country code and a mobile network code that is assigned to the network operator. Each SIM on the mobile communication device may support a subscription that is used to register with and communicate over a PLMN using a corresponding radio access technology (RAT). For example, a subscription may use a LTE RAT to communicate with a PLMN that supports LTE communication.
A network operator may operate more than one PLMN. Some of the PLMNs that belong to the same network operator may be considered to be equivalent such that a subscription belonging to the network operator may register with any of the equivalent PLMNs to communicate. For example, a network operator may operate a PLMN for GSM communication and another equivalent PLMN for UMTS communication. A subscription on a mobile communication device that belongs to the network operator and is capable of both UMTS and GSM communication may be able to register with either the UMTS or GSM PLMN to acquire network service.
A subscription on the mobile communication device may store an equivalent PLMN (EPLMN) database that lists the PLMNs considered to be equivalent by the network operator. The network operator may send the EPLMN database to a subscription on the mobile communication device through one of the PLMNs in the EPLMN database on which the subscription is registered. The EPLMN database may be stored and associated with the subscription. When the subscription attempts to acquire service from a network, the subscription may check the EPLMN database to determine all of the equivalent PLMNs that are available to the subscription. The subscription may select one of the PLMNs and register with the selected PLMN. The selection may depend on the RAT capabilities of the subscription compared with the EPLMNs available. For example, if a subscription is capable of GSM and UMTS communication, the subscription may select an EPLMN with UMTS capabilities because UMTS has a higher data communication rate than GSM.
A mobile communication device may have more than one SIM that supports more than one subscription. More than one subscription may belong to the same network operator, in which case the same EPLMNs should be available to each subscription. In other words, the EPLMN database for each subscription should be the same. However, in some cases the network operator may not send the EPLMN database to a subscription. In such cases, a user may switch from a first subscription that has the EPLMN database to a second subscription that does not have the EPLMN database. The first subscription does not advertise the EPLMN database to other subscriptions in the mobile communication device. This leads to an asymmetric EPLMN configuration because the second subscription may not be informed of all the PLMNs that are available. Thus, the second subscription may end up registering with a lower data communication rate PLMN (e.g., GSM) even through a higher data communication rate PLMN is available (e.g., UMTS).